Solar cell breakthrough could lead to battery-free devices

An international team, led by researchers at University College London (UCL), has developed a solar cell that is capable of harvesting energy from indoor light — meaning devices such as keyboards, remote controls, alarms and sensors could soon be battery-free.

To make the cell, the researchers used perovskite: a material that is being increasingly used in outdoor solar panels. However, unlike traditional silicon-based solar panels, perovskite has the potential to be used indoors as well, as its composition can be adjusted to better absorb the specific wavelengths of indoor light.

There’s a catch, though, as perovskite contains tiny defects in its crystal structure — known as ‘traps’ — which can cause electrons to get stuck before their energy can be harnessed. These defects not only interrupt the flow of electricity but also contribute to the material’s degradation over time.

In a study published in the journal Advanced Functional Materials, the team describes how they used a combination of chemicals to reduce these defects, potentially making perovskite indoor solar panels viable.

The team said that the perovskite photovoltaics they engineered are about six times more efficient than the best commercially available indoor solar cells. They are also more durable than other perovskite devices and could be used for an estimated five years or more, rather than just a few weeks or months.

“Billions of devices that require small amounts of energy rely on battery replacements — an unsustainable practice. This number will grow as the Internet of Things expands,” said senior author Dr Mojtaba Abdi-Jalebi, who is an Associate Professor at the UCL Institute for Materials Discovery.

“Currently, solar cells capturing energy from indoor light are expensive and inefficient. Our specially engineered perovskite indoor solar cell can harvest much more energy than commercial cells and is more durable than other prototypes. It paves the way for electronics powered by the ambient light already present in our lives,” he said.

Abdi-Jalebi said the team was currently in discussions with industry partners to explore scale-up strategies and commercial deployment.

“The advantage of perovskite solar cells in particular is that they are low-cost — they use materials that are abundant on Earth and require only simple processing. They can be printed in the same way as a newspaper.”

A major problem with earlier perovskite solar cells was a high density of traps in the material and its interfaces with charge-collecting layers, which disrupted the flow of charge and caused energy to be lost as heat.

To combat this challenge, the research team introduced a chemical, rubidium chloride, that encouraged a more homogeneous growth of perovskite crystals with minimal strains, reducing the density of traps.

Two other chemicals¹ were added to stabilise two types of ions (iodide and bromide ions), preventing them from migrating apart and bunching into different phases, which degrades the performance of the solar cell over time, again by disrupting the flow of charge through the material.

“The solar cell with these tiny defects is like a cake cut into pieces,” said lead author Siming Huang, a PhD student at UCL’s Institute for Materials Discovery. “Through a combination of strategies, we have put this cake back together again, allowing the charge to pass through it more easily. The three ingredients we added had a synergistic effect, producing a combined effect greater than the sum of the parts.”

Results

When put to the test, the team’s solar cells were found to convert 37.6% of indoor light (at 1000 lux — equivalent to a well-lit office) into electricity, which they said was a world record for solar cells that have been optimised for indoor light.²

The researchers also tested the solar cells to see how well they resisted degradation over time.

After more than 100 days, the newly engineered cells retained 92% of their performance, compared to a control device (perovskite whose flaws had not been reduced) that retained only 76% of its initial performance.

In a harsh test of 300 hours of continuous intense light at 55°C, the new solar cells retained 76% of their performance, while the control device dropped to 47%.

The team’s study can be read at DOI: 10.1002/adfm.202502152.

_{1. Organic ammonium salts N,N-dimethyloctylammonium iodide (DMOAI) and phenethylammonium chloride (PEACl).}

_{2. This sort of solar cell has a bandgap of 75 eV, which is tuned to absorb the higher-energy, mostly visible wavelengths of light emitted from indoor sources. The bandgap represents the minimum energy required to excite an electron so that it joins the electrical charge through the solar cell.}

Image caption: Associate Professor Mojtaba Abdi-Jalebi and PhD candidate Siming Huang with panels of their solar cells optimised for indoor light. Credit: UCL/James Tye